When Olivier Todd once asked Jean-Paul Sartre, Albert Camus' old Saint Germain des Pres intellectual sparring partner, which of Camus' books he liked best he said: 'The Fall, because Camus has hidden himself in it.'

With the publication of his massive biography, Albert Camus: A life, Todd does some serious unveiling of the Algiers slum kid who, at 43, became the second youngest Nobel Prize winner in history. Letters never before published reveal him as an obsessive womaniser.

The Fall (1956) is the confession of a celebrated Parisian lawyer brought to crisis when he fails to come to the aid of a drowning woman. The 'drowning woman' was Camus' second wife, Francine, who had a mental breakdown. As mother of his two children, Camus decided it would be more appropriate if her relationship with him was that of 'a sister', allowing him erotic freedom. For years she appeared to go along with this but then she cracked. Todd says that Francine said to her husband: 'You owed me that book,' and Camus had agreed.

The revelations in Todd's biography of Camus' womanising could hardly have come as a surprise to those who had read Camus' early non-fiction. His reflections on Don Juanism in The Myth Of Sisyphus, written when he was 28, read like both a confession and a declaration of future policy: 'It is because he (Don Juan) loves them with the same passion and each time with his whole self that he must repeat his gift and his profound quest,' Camus wrote.

'Why should it be essential to love rarely in order to love much?' he asked. And: 'What Don Juan realises in action is an ethic of quantity, whereas the saint, on the contrary, tends towards quality.'

He carried the philosophy further, claiming that a mother or an uxorious wife necessarily had 'an enclosed heart' because it is 'turned away from the world' to fasten on one object. But Don Juan's love was liberating.

In December 1959, Camus' womanising reached its apotheosis. On the 29th, he wrote to his mistress announcing that he would shortly be returning to Paris from Lourmarin, where he had spent the summer with his wife and children: 'This frightful separation will at least have made us feel more than ever the constant need we have for each other.' On the next day he wrote: 'Just to let you know I am arriving on Tuesday by car. I am so happy at the idea of seeing you again that I am laughing as I write.' A day later, he wrote: 'See you Tuesday, my dear, I'm kissing you already and bless you from the bottom of my heart.' There was yet another letter setting up a date in New York.

Apart from the unremitting ardour, there was one thing remarkable about these letters: they were all to different women. The first was to Mi, a young painter; the second to Catherine Sellers, an actress; the third to Maria Casares, an internationally famous actress with whom he had a liaison for 16 years; and the fourth was to an American, Patricia Blake.

When, over a period of five years, Olivier Todd got access to all of these letters, he faced a dilemma. Copyright of all Camus' letters is invested in his literary executor - his daughter, Catherine. 'It is one thing for children to know their father was a womaniser,' Todd says, 'but quite another to show them proof.'

There was one letter written, to an 'Yvonne' with whom he was having a passionate affair, on the eve of his marriage: 'I'm probably going to waste my life,' he wrote. 'I mean I am going to marry F' 'That was Catherine's mother,' says Todd. But Catherine Camus raised no objections.

Mi, who received the first of those December letters, was a young painter of Danish extraction. Camus met her in the traditional way, picking her up at the Cafe Flore in Saint Germain des Pres in 1957. She was one of the rare females with whom he shared his other passion - football.

Told that she had disappeared from circulation, Todd used a very unjournalistic device: he looked her up in the equivalent of the phone book, the Minitel. She had married, had a daughter and divorced. She will still only be identified as Mi.

Camus had met Maria Casares, later star of Cocteau's Orpheus but already an established actress, in 1944. Daughter of a rich Spanish Republican, a refugee from Franco, she was a passionate, wilful, intelligent woman. She was probably the only one of his lovers who had a relationship of equality with him. In addition, Todd says, 'If he was a Don Juan, she was a Don Juana'.

Casares, who died recently, wrote an autobiography in which she was candid about her celebrated relationship with Camus, but with a curious high-mindedness never quoted directly from his hundreds of letters.

And then there was the avant-garde actress and theatre director, Catherine Sellers. In James Kent's Bookmark biography of Camus, based on Todd's book and shown on BBC2, we saw an actor playing a scene from The Fall. The actor is Sellers' husband. So Camus' former lover had her husband play the part of the hero of The Fall who was of course a version of Camus.

The New York letter was to Patricia Blake, whom Camus had met when he visited the US in 1946. She was then 20 and a copywriter for Vogue. She became his guide to the city, initially impressed by the gentlemanly distance at which he held his partners during the foxtrot. She was having lunch with him in Paris in 1957 when he received the news that he had won the Nobel Prize. He confessed to her that he felt suffocated.

With good reason. The Nobel committee, indulging their usual political meddling, gave the prize to a 'Frenchman of Algeria' at a high point in the Algerian war. Camus felt he could not turn it down. He was instantly derided by most of the Parisian intellectual elite. (Later, in the sixties, Sartre was to refuse it).

Camus kept none of these planned rendezvous. Driving back to Paris with his publisher and friend Michel Gallimard, their car hit a tree and he was killed instantly. He was 46.

Far from being a Parisian intellectual with little conscience about his affairs, Camus' relationships were important to him. 'He had a much more healthy relationship with women than Sartre,' Todd says. 'His relationships were quite moving'.

Camus was no Parisian sophisticate. He was a working-class pied-noir (born in Algeria but of European origin). His father died of war wounds when he was an infant; his mother was a charlady with no talent for communication, emotional or intellectual. In addition, something overlooked because of his colossal energies, he was chronically tubercular and must have had a perpetually feverish will to live. He also had a brief, early and disastrous marriage in 1934 to a drug addict, Simone Hei.

It is not hard to detect profound emotional deprivation in that background, of the kind projected in The Outsider (1942) in which the hero does not seem to be able to see the point of love and shoots an Arab without knowing why. But you cannot convincingly attach a lugubrious alibi to a personality of such rigorous honesty as Camus: the communist who, unlike Sartre, condemned Stalin's labour camps when their existence was revealed; and the consumptive journalist who worked in occupied Paris for the clandestine paper, Combat, while the upper-class spokesman for communism, Sartre, led an unmolested life of intellectual and material ease.

'It is an error,' Camus wrote, 'to make Don Juan an immoralist: in this respect he is like everyone else. He has the moral code of his sympathies and his antipathies'.